FRIDAY, Feb. 1 (HealthDay News) -- Mild winters where few people catch the flu tend to be followed by serious flu outbreaks the next year, a new study finds, suggesting that global warming could mean harsher flu seasons ahead.
That, at least, is the theory. The study, which appeared Jan. 28 in the journal PLoS Currents: Influenza, shows a correlation between warm U.S. winters and more flu misery the following winter.
"But correlation doesn't mean causation," said lead researcher Sherry Towers, a research professor at Arizona State University, in Tempe.
"The dynamics that cause a severe flu season are so multifactorial," Towers said. One example is whether the flu shot for a particular season is a good match for the flu strains that are actually circulating. (To formulate the flu vaccine every year, scientists have to predict which strains will predominate in the upcoming season.)
Still, Towers said her findings offer "compelling evidence" of a link between mild winters and extra flu misery the next time around.
For the study, she and her colleagues looked at U.S. government data for each flu season since 1997. They found an interesting pattern, Towers said: When a winter had above-average temperatures, the flu season the following fall and winter was more severe than normal 72 percent of the time.
Normally, flu season in the United States peaks in late January or early February. But Towers's team found that the flu season following a mild winter was 80 percent more likely than normal to peak before Jan. 1.
This year's rough flu season is a case in point, Towers said.
The nation saw an early start to this flu season, with cases taking off in November. Last week, the U.S. Centers for Disease Control and Prevention reported that flu activity across the country was still higher than average, although it was leveling off in some areas.
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